In recent years, information theft and the like by targeted email attacks has been increasing as cases of cyber-attack. As an example of technology related to countermeasures against targeted email attacks, there is technology that detects spoofed email from an unauthorized terminal by appending identification information (for example, a MAC address) of the terminal that is the transmission source of an email in the email header when transmitting and receiving email.
Technology also exists that, based on the receiving history at the receiving side, detects spoofed email sent by the attacking side using an unauthorized personal computer (PC) or network.
However, such technology references identification information of the transmission source terminal against permitted identification information, and is not able to detect spoofed email that forges the transmission source information.
There has therefore been a proposal to attach biometric traits acquired from a terminal user to email before transmission, and to determine whether or not email is from an authorized terminal that the user is permitted to use. For example, technology has been proposed in which voice trait patterns in a password spoken by the sender are appended to electronic mail, and the appended voice trait patterns are compared to reference-use voice trait patterns of the sender themselves that were received in advance at the side of the receiver of the electronic mail. In such technology, the terminal that is the transmission source of the electronic mail is determined whether terminal that the sender is permitted to use.